docs: def _get_hanging_wall_coeffs_rrup(self, dists):
          """
          Returns the hanging wall rrup term defined in equation 13
          """
          fhngrrup = np.ones(len(dists.rrup))
          idx = dists.rrup > 0.0
          fhngrrup[idx] = (dists.rrup[idx] - dists.rjb[idx]) / dists.rrup[idx]
          return fhngrrup